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CA3160E Fiches technique(PDF) 6 Page - Intersil Corporation |
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CA3160E Fiches technique(HTML) 6 Page - Intersil Corporation |
6 / 17 page 6 magnitude as those encountered in an operational amplifier employing a bipolar transistor input stage. The 2V differential voltage example represents conditions when the amplifier output state is “toggled”, e.g., as in comparator applications. Power Supply Considerations Because the CA3160 is very useful in single supply applications, it is pertinent to review some considerations relating to power supply current consumption under both single and dual supply service. Figures 1A and 1B show the CA3160 connected for both dual and single supply operation. Dual-supply operation: When the output voltage at Terminal 6 is 0V, the currents supplied by the two power supplies are equal. When the gate terminals of Q8 and Q12 are driven increasingly positive with respect to ground, current flow through Q12 (from the negative supply) to the load is increased and current flow through Q8 (from the positive supply) decreases correspondingly. When the gate terminals of Q8 and Q12 are driven increasingly negative with respect to ground, current flow through Q8 is increased and current flow through Q12 is decreased accordingly. Single supply operation: Initially, let it be assumed that the value of RL is very high (or disconnected), and that the input- terminal bias (Terminals 2 and 3) is such that the output terminal (No. 6) voltage is at V+/2, i.e., the voltage-drops across Q8 and Q12 are of equal magnitude. Figure 18 shows typical quiescent supply-current vs supply voltage for the CA3160 operated under these conditions. Since the output stage is operating as a Class A amplifier, the supply current will remain constant under dynamic operating conditions as long as the transistors are operated in the linear portion of their voltage-transfer characteristics (see Figure 17). If either Q8 or Q12 are swung out of their linear regions toward cutoff (a non-linear region), there will be a corresponding reduction in supply-current. In the extreme case, e.g., with Terminal 8 swung down to ground potential (or tied to ground), NMOS transistor Q12 is completely cut off and the supply current to series connected transistors Q8, Q12 goes essentially to zero. The two preceding stages in the CA3160, however, continue to draw modest supply-current (see the lower curve in Figure 18) even though the output stage is strobed off. Figure 1A shows a dual-supply arrangement for the output stage that can also be strobed off, assuming RL = ∞, by pulling the potential of Terminal 8 down to that of Terminal 4. Let it now-be assumed that a load resistance of nominal value (e.g., 2k Ω) is connected between Terminal 6 and ground in the circuit of Figure 1B. Let it further be assumed again that the input-terminal bias (Terminals 2 and 3) is such that the output terminal (No. 6) voltage is at V+/2. Since PMOS transistor Q8 must now supply quiescent current to both RL and transistor Q12, it should be apparent that under these conditions the supply current must increase as an inverse function of the RL magnitude. Figure 20 shows the voltage-drop across PMOS transistor Q8 as a function of load current at several supply voltages. Figure 17 shows the voltage transfer characteristics of the output stage for several values of load resistance. Wideband Noise From the standpoint of low-noise performance considerations, the use of the CA3160 is most advantageous in applications where in the source resistance of the input signal is on the order of 1M Ω or more. In this case, the total input-referred noise voltage is typically only 40 µV when the test circuit amplifier of Figure 2 is operated at a total supply voltage of 15V. This value of total input-referred noise remains essentially constant, even though the value of source resistance is raised by an order of magnitude. This characteristic is due to the fact that reactance of the input capacitance becomes a significant factor in shunting the source resistance. It should be noted, however, that for values of source resistance very much greater than 1M Ω, the total noise voltage generated can be dominated by the thermal noise contributions of both the feedback and source resistors. 7 3 2 8 4 6 V+ - + CA3160 NEGATIVE SUPPLY OUTPUT RL STAGE Q12 Q8 V- FIGURE 1A. DUAL POWER SUPPLY OPERATION 7 3 2 8 4 6 - + CA3160 OUTPUT RL STAGE Q12 Q8 V+ FIGURE 1B. SINGLE POWER SUPPLY OPERATION FIGURE 1. CA3160 OUTPUT STAGE IN DUAL AND SINGLE POWER SUPPLY OPERATION CA3160, CA3160A |
Numéro de pièce similaire - CA3160E |
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Description similaire - CA3160E |
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